1. Field of the Invention
The present invention relates to a method of sealing electronic parts with a resin.
2. Description of the Related Art
In the field of packages for microelectronics, so far, it has been widely accepted practice to seal electronic parts [CSP (Chip Scale Package), COB (Chip On Board), PLCC (Plastic Leadless Chip Carrier), BGA (Ball Grid Array), TAB (Tape Automated Bonding), etc.] with a resin. A representative example has been disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 4-346235 according to which a sealing resin is porous plate-printed (screen-printed) generally in an open atmosphere.
In recent years, however, the content of a filler component in the resin has been increased from the standpoint of improving reliability of the sealing. Besides, due to its thixotropic property, the resin exhibits further increased viscosity. It is, therefore, becoming difficult to introduce the resin by smoothly passing it through very small gaps between densely bonded wires without causing damage to the wires.
Accordingly, the lower portions of the wires (e.g., portions A1, A2 in FIG. 1) that are densely bonded are not filled with the sealing resin but air remains to form voids. Or, due to the voids and local settlement of the resin, the sealing resin is not flat on the surface or lacks dimensional precision.
Therefore, it has been proposed to effect porous plate-printing in vacuum as disclosed in, for example, Japanese Examined Patent Publication (Kokoku) No. 6-66350. Even though porous plate-printing is effected in vacuum, however, it is not possible to eliminate the above-mentioned defects, such as the difficulty in introducing the resin by smoothly passing it through very small gaps among the densely bonded wires without causing damage to the wires.